Braking system is an important component of automotives. Currently, conventional one-piece-cast drum-type brake is widely applied in vehicles.
In the prior art, a typical drum-type brake comprises a brake drum and brake shoes that will get into contact with the inner side surface of the brake drum. The brake drum is rotating when the vehicle is being driven. Should braking be needed, brake shoes will press against the brake drum under the brake force and convert the kinetic energy of moving vehicle into heat energy by making use of the frictional resistance against the brake drum, thus slowing down or even stopping a moving vehicle to ensure driving safety.
When a vehicle is loaded and driving at a high speed, particularly on a long downward road or a steep slope, the need for a greater brake force and continual braking actions to control the vehicle will increase the temperature on the interior wall of the brake drum drastically, giving rise to an increased difference in temperature inside and outside the brake drum and crippling subsequently the mechanical properties of materials at high temperature. As a traditional material for one-piece cast brake drum, gray cast iron is characterized by low strength and brittleness. In order to alleviate the negative impact of these characteristics in this case, the wall of a brake drum must be thick enough so that the brake drum can have a higher structural strength as a whole. However, the thicker the wall of the brake drum is, the greater the temperature difference will be when the brake drum is braking. An increased temperature difference will give rise to a thermal stress, which plus deteriorated mechanical properties of the material at high temperature will often lead to a cracked interior wall of the drum from longitudinal micro-cracks, then a cracked drum, and even final break. Therefore, a traditional one-piece cast brake drum usually has a relatively short life and poor safety performance.
U.S. Pat. Nos. 5,782,324 and 6,196,363 (Wall) propose a composite brake drum and method of making a brake drum consisting of two layers: a one-piece mounting flange and shell and a liner cast integrally in the shell. This structure is disadvantageous.
In summary, how to improve the structural strength, thermal conductivity, life and safety of the brake drum has become a problem needed to be solved.